The present invention relates to a penetrameter positioner for bore-side radiography of tubes and more particularly to an improved positioner for providing easy insertion or removal of the positioner to or from the desired point of inspection and including means for placing the penetrameter against the tubing wall at the point of inspection. It is the result of a contract with the U.S. Department of Energy.
An image-quality indicator (IQI), otherwise known as a penetrameter, is needed in radiographic examination to assure a consistent image. American industry commonly uses a plaque consisting of a thin shim with right-cylindrical holes. Both the thickness of the shim and the diameter of the holes are fractional parts of the specimen thickness (such as 2%). However, there are usually minimum dimensions on the penetrameter which reduce its validity and usefulness for thin materials, typically less than about 6.0 mm (1/4 inch). A further complicating factor for radiography of tube-to-tubesheet joints with a coaxial radiation source is that adequate film densities are normally achieved only in the immediate vicinity of the weld. For its image to show, the penetrameter would need to be placed on the weld. However, such placement would confuse the interpretation because the image of the penetrameter holes would be superimposed on the image of the weld.
Another type of penetrameter is also used, particularly in Europe. This penetrameter contains small-diameter wires and can be superimposed on a weld without confusing the interpretation.
For radiography the penetrameters are placed source-side of the weld, if possible. In bore-side inspection of tubing welds, the placement of the penetrameters is on the outer surface of the target holder for x-radiography and on the outer surface of the source tube for isotope radiography. Film for recording the penetrating radiation is placed exterior to the tube weld using a cassette such as that described in U.S. Pat. No. 3,952,204, to Earl V. Davis et al, issued Apr. 20, 1976. Since the weld may be located several meters from an end of the tubing, sufficient clearance must be permitted about the penetrameter holder to permit easy insertion or removal of the radiation source. Different values of clearance may be experienced when tubing diameter varies. This clearance, however, prevents placing the penetrameter in close proximity to the weld and thus reduces resolution of the penetrameter image.
It is, therefore, an object of the present invention to provide a device for easily positioning a penetrameter (and source of radiation) into and from long tubing and yet permit placing the penetrameter in close proximity to the weld surface to be radiographed.
Other objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following detailed description of a preferred embodiment of the invention and the accompanying drawings.